Conventional automatic machine dishwashing compositions are normally phosphate-based, highly alkaline products comprising a chlorine bleaching agent having a solution pH generally above 12.0. Though performance-wise these conventional products are quite satisfactory, they have some serious drawbacks in other aspects. First of all, highly alkaline compositions have the disadvantage of being aggressive and hazardous. Incorporation of chlorine bleaches, though effective for stain removal, requires special processing and storage precautions to protect the composition components from decomposition upon direct contact with active chlorine.
The stability of chlorine bleach is also critical and raises additional processing and storage difficulties. A further disadvantage is the difficulty of dyeing and perfuming of such compositions owing to incompatibility of many dyes and perfumes with chlorine. Finally, phosphate and phosphorus-containing components have been under attack, because of the general belief that they can lead to environmental problems.
It has been suggested that these drawbacks be overcome by formulating a reduced phosphate or phosphate-free machine dishwashing composition of lower alkalinity and using a milder oxygen bleach instead. To compensate reduced performance, particularly with respect to starch and protein removal, enzymes are added, especially amylolytic and proteolytic enzymes, such as amylases and proteases. The oxygen bleach used therein is sodium perborate or sodium percarbonate in conjunction with an organic activator or bleach precursor, e.g. N, N, N', N'-tetraacetylethylene diamine (TAED), which upon dissolution will react to form an organic peroxyacid, e.g. peracetic acid, as the bleaching species.
However, the performance of such mildly alkaline enzymatic dishwashing compositions is still far from ideal. Oxygen bleaches are generally poorer bleaching agents compared with chlorine bleaches. The use of an activated perborate for achieving a reasonable bleach performance, especially on tea stains, appears to be at the expense of the starch removal, due to incompatibility of amylases with stronger bleaching agents. Use of perborate alone, i.e. without TAED, would improve the starch removal, but the bleach performance is poor. It is thus the incompatibility of enzymes, particularly of amylases, with the bleach, that forms a major problem in the formulation of a satisfactory machine dishwashing composition comprising an oxygen bleach and enzymes.
Consequently, it is an object of the present invention to provide a machine dishwashing composition containing a peroxygen compound as the bleaching agent that will combine improved bleaching action with excellent starch removal properties.